linux-ext4 - Re: [PATCH] ext4: direct return when jinode allocate failed

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Message-ID: <20181016190840.GF24131@thunk.org>
Date:   Tue, 16 Oct 2018 15:08:40 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     fishland <fishland@...yun.com>
Cc:     adilger.kernel@...ger.ca, wang.yi59@....com.cn,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        Liu Song <liu.song11@....com.cn>
Subject: Re: [PATCH] ext4: direct return when jinode allocate failed

On Tue, Oct 16, 2018 at 10:55:26PM +0800, fishland wrote:
> The jinode does not need protected by *i_lock*, we can return
> directly if memory allocation fails.
> 

I don't see anything wrong with this patch, but at the same time, I'm
not sure I see the benefit, either.  Checking for the allocation
failure is cheap, and moving it out spinlock doesn't buy much; not to
mention that the allocation failure is going to be highly uncommon.

What inspired this commit?

						- Ted



> Signed-off-by: Liu Song <liu.song11@....com.cn>
> Reviewed-by: Wang Yi <wang.yi59@....com.cn>
> ---
>  fs/ext4/inode.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index d767e993591d..67ba6f062de5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4384,12 +4384,11 @@ int ext4_inode_attach_jinode(struct inode *inode)
>  		return 0;
>  
>  	jinode = jbd2_alloc_inode(GFP_KERNEL);
> +	if (!jinode)
> +		return -ENOMEM;
> +
>  	spin_lock(&inode->i_lock);
>  	if (!ei->jinode) {
> -		if (!jinode) {
> -			spin_unlock(&inode->i_lock);
> -			return -ENOMEM;
> -		}
>  		ei->jinode = jinode;
>  		jbd2_journal_init_jbd_inode(ei->jinode, inode);
>  		jinode = NULL;
> -- 
> 2.17.1
>